Biologia, Bratislava, 57/Suppl. 11: 197-202, 2002.
ISSN 0006-3088 (Biologia).
Characterization of the functional module responsible for the low temperature optimum of a rice a-amylase (Amy 3E).
Rei Abe, Yogo Chiba & Tasuku Nakajima*
Division of Life Science, Graduate School of Agriculture, Tohoku University, Tsutsumidori-Amamiyamachi, Sendai,-shi, 981-8555, Japan; fax: 81-22-717-8778, e-mail: email@example.com
* corresponding author
Received: October 4, 2001 / Accepted: February 12, 2002
Cultured cells of rice produce two a-amylase isozymes, AMY-I(Amy 1A) and AMY-III(Amy 3E). Eight chimeric genes, constructed from various combination of AMY-I and AMY-III cDNA fragments, were expressed using a bacterial expression system, and each recombinant chimeric protein was characterized. Four of the eight recombinant enzymes, having region c (one of the four regions having unconserved base sequences between AMY-I and AMY-III cDNAs) of AMY-I, showed the same enzyme characteristics as those of native AMY-I, which had a high temperature optimum at 50 oC. The other four chimeric proteins carrying region c of AMY-III showed AMY-III type characteristics and exibited a low temperature optimum at 25 oC. These results suggest that the region c (Phe179–Trp205: a-helix-4, b-sheet-5, a-helix-5) is responsible for the property of the low temperature optimum of AMY-III.
Key words: plant a-amylases, cultured-rice cells, chimeric enzymes.